Electric blasting cap



y 9, 1940- E. WATTS 2,207,137

ELECTRIC BLASTING CAP Filed Jan. 24, 1939 INVENTOR. EDWA RD L. WATTS BY ATTORNEY Patented July 9, 1940 ELECTRIC BLASTING CAP Edward L. Watts, Oakland, .Callf.,

California Cap Company, Oaklan corporation of Galifo mm. to d, Calm, a

Application January 24, 1939, Serial No. 252,559 6 Claims. (01. 102-16) .1 drawing.

In the drawing the figure is a greatly enlarged longitudinal cross section of an electric blasting cap constructed in accordance with my invention.

In the early construction of blasting caps they were comparatively simple in consisting of a cylindrical metal shell, loaded at the closed end with a fulminate or other sensitive detonating explosive and which was go fuse, or by an electric igniter or electric match head.

'In recent years the trend in the manufacture of blasting caps has been towards the use of several layers of explosives of varying degrees 5 of detonating quality. The base charge in the cap (principally relied upon to set off the dyna mite or other disrupting explosive with which the cap is used) being selected for its detonating efiiciency with respect to the main explosive, and

so it is this yp tion inore particularly pertains and is shown. in

the drawing.

In the drawing A represents an inner thin metal shell as of copper alloy as usually used in blasting cap manufacture, which contains within it the complete assemblage of elements required to make an electric blasting cap of the type mentioned.v Thus within its closed lower end is a base charge B of a relatively insensitive detonat- 40 lug-compound such as tetryl (tetranitromethylanilene), trinitro toluene, nitro mannite, picric acid, or any others, or admixtures, while above this is a more sensitive primary detonating compound C such as mixtures of mercury fulminates,

lead azide, chlorate, nitro-mannite and/or othermodifying compounds all well known in the art. Above the primary compound may be positioned an electric matc -head E made by coating or covering a resistance element with an ignition compound, or a flash compound such as can be readily ignited by the heated resistance element which may project into it, or the primary detonating compound may be in whole or in part so compounded and adapted as to be easily ignited l by the electric resistance element which may pro-- set 011 either by a powder of blasting cap to which the invenject into it. The drawing refers to the first mentioned type of construction. Also shown in the drawing is a centrally perforated inverted capsule? confining the primary detonating compound 0, though the use of this 5 is optional insofar as the present invention is concerned. The electric lead wires F pass upward through a suitable plug G as is customary, then through a sealing compound H which is generally of an m asphaltic or other waterproof nature, poured in, in a molten condition, to harden, while on top of the sealing compound His a closing plug I generally of sulphur poured in while molten so as to interlock into an outwardly formed cir- 15 cumferential groove J in the wall of the shell to prevent any displacement of the layers.

' So far described the inner shell A with its contents constitutes an electric blasting cap of well known type of which a number of examples more go or less modified are readily obtainable on the market.

Surrounding this inner can A, however, is an outer metallic shell- K, as of thin drawn copper alloy or other blasting cap metals, and with an 5 inner diameter adapted to substantiallytouch the lower end of the inner shell A as indicated, and the surface of the outer wall of the annular groove J of the inner shell, thus making the outer shell of slightly tapering form, (since groove J .is

very shallow) and spaced slightly from the innershell for most of the latters length. The outer shell may-be cylindrical, but the form shown is preferable.

The outer shell extends for a distance below as the inner shell and is filled at that point with a base detonating charge L, preferably of the same character as the base charge 13 carried by the inner shell.

Above the ring J the outer shell K'is flied with 40 a sealing compound M preferably of the same character as the sealing compound H in the inner shell, while above the compound M isv another closure plug N locked in-'place. by an annular groove 0. This plug is preferably of the same ,46

composition as plug I.

The quantity of the base chargeL confined in the lower end of the outer shell may be greater or smaller than the quantity B within the inner shell depending o the detonating effect required, '50 and may if desired, be a base charge of greater detonating quality than base charge B.

As a modification of the above structure the inner shell A may have its sides straight with inner shell is as- 5 out the groove J, and when the The upper closure plug N locked in place by the annular groove 0 will hold the assemblage together.

Blasting caps constructed in the manner shown and described have been found to have greatly increased detonating efiiciency, especially in deep hole geophysical prospecting for oil, where great pressures are met with which sometimes cause failure of standard blasting caps. The double seal construction also provides against any possible intrusion of water at great depth and pressures to which caps are subjected in such operations. In fact these improved caps are largely supplanting common caps in such work. They are of course to be embedded in the dynamite, gelatine or other explosive in the usual way.

An important advantage secured by the use of double shell construction is that a very long double sealed and double plugged assemblage is had above the electric match head yet each section of sealing compound (H and M) is poured into a relatively shallow chamber since the inner shell A is completed before inserting into the outer shell K;

Having thus described my improved blasting cap construction what I claim is:

1. A blasting cap comprising a pair of nested tubular blasting cap shells each having-a closed lower end and an open upper end and with the bottom wall of the outer shell spaced below the bottom wall-of the inner shell, a base detonating charge confined in the lower portion of the inner shell and electric ignition means including a primary charge above said base charge with lead Wires extending upwardly and out, means above the ignition means filling and sealing the shell space and sealing around the wires, and a base detonating charge confined in theouter shell space be low the innershell.

2. A blasting cap comprising a pair of nested tubular blasting cap shells each having a closed lower endand an open upper end and with the bottom wall oi the outer shell spaced below the bottom wall of the inner shell and the open end of the outer shell extending above the open end of the inner shell, a base detonating charge confined in the lower portion of the inner shell and electric ignition means including i a primary charge above said extending upwardly and out of both shells, means above theignition means filling and sealing the shell space and sealing around the wires, and a base detonating charge confined in the outer shell space below the inner shell.

3. A blasting cap comprisifi a. pair of nested tubular blasting cap shells e h having a closed lower end and an open upper end and with the base charge with lead wires snugly the outer wall bottom wall of the outer shell spaced below the of the inner shell, a base detonating charge confined in the lower portion of the inner shell and electric ignition means including a primary charge above said base charge with lead wires extending upwardly and out of bothshells, means above the ignition means filling and sealing the shells and sealing around the wires and abase detonating charge confined in the outer shell space below the inner shell, the filling and sealing means in the inner shell including a waterproof adhesive plastic compound cast in place, and a similar compound cast in place in the outer shell.

4. A blasting cap comprising a pair of nested tubular blasting cap shells each having a closed lower end and an open upper end and with the bottom wall of the outer shell spaced below the bottom wall of the inner shell and the open end of the outer shell extending above the open end of the inner shell, a base detonating charge confined in the lower portion of the inner shell and electric ignition means including a primary charge above said'base charge with lead ing upwardly and out of both shells, means above the ignition means filling and sealing thev shells and sealing around the wires, and a base detonating charge confined in the outer shell space below the inner shell, the filling and sealing means in the inner shell including a waterproof adhesive plastic compound cast in place, and a similar compound cast in place in the outer shell separated by a closure plug positioned in the upper end of the inner shell.

5. A blasting cap comprising a pair of nested tubular blasting cap shells each having a closed .lower end and an open upper end and with the bottom wall of the outer shell spaced below the bottom wall of the inner shell and the open end of the outer shell extending above the open end of the inner shell, abase detonating charge confined-in the lower portion of the innershell and electric ignition means including a primary charge above said base charge with lead wires extending upwardly and out of both shells, means above separated by a closure plug positioned in the up- ,per end of the inner shell, and a closure plug within the outer end of the outer shell.

6. In a double shell blasting cap asset out in claim 2,- said outer shell being slightly tapered smaller I toward its lower end and embracing inner shell.

L. WA'ITS.

wires extend- 01' the lower end of the 

